This is not a rumor but a fact: marine animals modify their behavior during a solar eclipse.
For example, zooplankton reacts to the progressive decrease in brightness in the same way as at nightfall: it ascends the water column to get closer to the surface. Some similar observations have been made on fishes, and can be found on this short article by S. G. Reebs.
But what we can find on this particular subject is mostly missing scientific data due to the scarcity of this type of event. It would be extremely interesting to make observations on organisms directly dependent on light, such as heliophilic corals.
But I think I just missed my chance by letting pass the solar eclipse today (August 21, 2017, too busy to take pictures of the solar masked star). In any case, there are not many corals to study in Florida, since more than 90% of the coral reefs have bleached and / or died because of pollution and tourism activities since the 1970s ...